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Cross-bridge theory states that actin and myosin form a protein complex (classically called actomyosin) by attachment of myosin head on the actin filament, thereby forming a sort of cross-bridge between the two filaments. The sliding filament theory is a widely accepted explanation of the mechanism that underlies muscle contraction.
Cross-bridge cycle. Cross-bridge cycling is a sequence of molecular events that underlies the sliding filament theory. A cross-bridge is a myosin projection, consisting of two myosin heads, that extends from the thick filaments. [1] Each myosin head has two binding sites: one for adenosine triphosphate (ATP) and another for actin.
This process aligns actin and myosin filaments for efficient cross-bridge formation while also recruiting myosin heads from dormant states into contraction-ready configurations. [ 6 ] [ 10 ] Additionally, stretching the sarcomeres sensitizes the thin (actin) filaments to calcium, promoting stronger and more sustained contractions. [ 6 ]
The mechanism in which external factors stimulate growth and rearrangement is not yet fully understood. A number of growth factors and neurohumoral agents influence smooth muscle growth and differentiation. The Notch receptor and cell-signaling pathway have been demonstrated to be essential to vasculogenesis and the formation of arteries and veins.
Specifically, it increases the rate of phosphate release from myosin by stabilizing the pre-powerstroke and the phosphate release states, [8] thereby accelerating the rate-determining step of the cross-bridge cycle, which is the transition of the actin-myosin complex from the weakly bound to the strongly bound state.
The chakana (Andean cross, "stepped cross" or "step motif" or "stepped motif") is a stepped cross motif used by the Inca and pre-incan Andean societies. The most commonly used variation of this symbol today is made up of an equal-armed cross indicating the cardinal points of the compass and a superimposed square.
In a plate girder bridge, the plate girders are typically I-beams made up from separate structural steel plates (rather than rolled as a single cross-section), which are welded or, in older bridges, bolted or riveted together to form the vertical web and horizontal flanges of the beam. In some cases, the plate girders may be formed in a Z-shape ...
The stubs at the eastern end of the Dunn Memorial Bridge give a good cross section of girder bridge construction. A rolled steel girder is a girder that has been fabricated by rolling a blank cylinder of steel through a series of dies to create the desired shape. These create standardized I-beam and wide flange beam [7] shapes up to 100 feet in ...